Electric storage batteries have been in use for many years. Probably the most common use is in emergency or portable lighting devices such as the ordinary flashlight. The quality of the batteries has improved steadily along with the numbers of different applications for their use.
One of the more significant improvements is the development and commercial availability of rechargeable batteries, such as nickel-cadmium and sealed lead-acid batteries. Devices utilizing rechargeable batteries are frequently marketed with built-in charging circuits and provision for plugging into an electric wall outlet for recharging between periods of use.
It is frequently the case, however, that a battery operated device is called for in a given application because it involves operation in a remote area where electric power is not available. In many such applications, some form of recharging capability is particularly desired.
Consider, for example, flashlights, lanterns and other battery operated lighting devices which are carried for emergency use in lifeboats, planes, ships and various types of land vehicles. In a serious emergency, the user might become isolated for days or even weeks in a remote area. Without a recharging capability, the batteries can become depleted before help arrives. In such a situation, a means for recharging a flashlight or other signalling means could well make the difference between life and death.
Numerous other uses exist for a remote area recharging capability for small batteries. Examples include security devices for remote locations, remote repeater stations, beacons for navigational buoys at sea, emergency radios or other types of communications equipment, and various types of armed forces equipment employed on extended scouting forays.
An important need thus exists for a battery that may be recharged conveniently in a remote area. Because other electrical power sources are generally not available to provide the energy for recharging, some other source, such as solar energy, will have to be employed.